Recently, for the purpose of improving various types of performances such as gas barrier properties, various multilayered structures have been proposed in which a plurality of resin layers are laminated, each layer having a thickness of micron or submicron order. In particular, laminated films having an ethylene-vinyl alcohol copolymer layer have been used in applications such as packaging materials for food and medical applications, taking advantages of their superior gas barrier properties, stretchability, thermoformability and the like.
Conventional multilayered structures in which a plurality of layers including such an ethylene-vinyl alcohol copolymer layer, which were proposed taking into consideration gas barrier properties, and developed for the purpose of improving various characteristics include, for example (1) a multilayered structure having two ethylene-vinyl alcohol copolymer layers having different ethylene contents and degrees of saponification, with one layer containing a boron compound (see Japanese Unexamined Patent Application, Publication No. H5-31863), (2) a multilayered structure having layers constituted with a composition containing at least two types of ethylene-vinyl alcohol copolymers having different ethylene contents, with at least one face of the layer having a thermoplastic resin layer (see Japanese Unexamined Patent Application, Publication No. H2-261847), and the like.
The conventional multilayered structure (1) described above has an improved heat sealing property while maintaining gas barrier properties and non adsorptivity of the contents. Moreover, the conventional multilayered structure (2) described above also has improved formability while maintaining gas barrier properties. However, these multilayered structures do not satisfy further improvement of gas barrier properties, and are accompanied by disadvantages that significant deterioration of gas barrier properties, etc., is inevitable upon deformation such as flexion and/or stretching.